In particular, the bus cable comprises two leads. The data transmission is performed via the bus cable consistent with the communication protocol, and also the subscriber units connected to the bus cable are supplied with electrical power. A communication control device is disposed for controlling the communication consistent with the communication protocol.
A bus communication device has been known, for example, from publication DE 10 2010 037 262 A1. This bus communication device comprises an integrated bus control and energy supply device. As a result of this, a transmission of electrical energy in the form of dc current or also in the form of digital signals is possible on a shared bus line. This is referred to as a field bus system.
The simultaneous transmission of data signals on energy supply lines is also known in LAN networks, for example for the use in private homes, via so-called power-line adapters.
Publication WO 2009/063213 A1 describes a communication device with a bus line to which is connected a communication control device or a master computer and in which case at least one subscriber unit is connected by means of a coupling arrangement. In addition, a bus diagnostic unit is connected to the bus line. The coupling arrangement is also connected to a connected subscriber unit via a branch line. Furthermore, the coupling arrangement comprises a subscriber diagnostic unit in order to detect errors in a subscriber unit or in the branch line. The subscriber diagnostic unit controls a spur means that causes a condition on the bus line that deviates from the prespecified values in that it can be detected by the bus diagnostic unit as a deviation. Consequently, an error in a subscriber unit can also be detected and indicated via the bus diagnostic unit even if, for example, a galvanic separation has been established between the bus line and the branch line. The spur means may establish, for example, a low-ohmic connection between a core of the bus line and a ground connection or feed a signal between shielding and bus cores.